sdcard: a program to create a "virtual" /sdcard pointed at a path
sdcard is a program that uses FUSE to emulate FAT-on-sdcard style
directory permissions (all files are given fixed owner, group, and
permissions at creation, owner, group, and permissions are not
changeable, symlinks and hardlinks are not createable, etc.
usage: sdcard <path> <uid> <gid>
It must be run as root, but will change to uid/gid as soon as it
mounts a filesystem on /sdcard. It will refuse to run if uid or
gid are zero.
Change-Id: I9a5d2e5daaebeee632f8470172cbb77b7fa689f8
Signed-off-by: Brian Swetland <swetland@google.com>
diff --git a/sdcard/sdcard.c b/sdcard/sdcard.c
new file mode 100644
index 0000000..5d19604
--- /dev/null
+++ b/sdcard/sdcard.c
@@ -0,0 +1,752 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/uio.h>
+#include <dirent.h>
+
+#include "fuse.h"
+
+/* README
+ *
+ * What is this?
+ *
+ * sdcard is a program that uses FUSE to emulate FAT-on-sdcard style
+ * directory permissions (all files are given fixed owner, group, and
+ * permissions at creation, owner, group, and permissions are not
+ * changeable, symlinks and hardlinks are not createable, etc.
+ *
+ * usage: sdcard <path> <uid> <gid>
+ *
+ * It must be run as root, but will change to uid/gid as soon as it
+ * mounts a filesystem on /sdcard. It will refuse to run if uid or
+ * gid are zero.
+ *
+ *
+ * Things I believe to be true:
+ *
+ * - ops that return a fuse_entry (LOOKUP, MKNOD, MKDIR, LINK, SYMLINK,
+ * CREAT) must bump that node's refcount
+ * - don't forget that FORGET can forget multiple references (req->nlookup)
+ * - if an op that returns a fuse_entry fails writing the reply to the
+ * kernel, you must rollback the refcount to reflect the reference the
+ * kernel did not actually acquire
+ *
+ *
+ * Bugs:
+ *
+ * - need to move/rename node on RENAME
+ */
+
+#define FUSE_TRACE 0
+
+#if FUSE_TRACE
+#define TRACE(x...) fprintf(stderr,x)
+#else
+#define TRACE(x...) do {} while (0)
+#endif
+
+#define ERROR(x...) fprintf(stderr,x)
+
+#define FUSE_UNKNOWN_INO 0xffffffff
+
+struct handle {
+ struct node *node;
+ int fd;
+};
+
+struct dirhandle {
+ struct node *node;
+ DIR *d;
+};
+
+struct node {
+ __u64 nid;
+ __u64 gen;
+
+ struct node *next;
+ struct node *child;
+ struct node *all;
+ struct node *parent;
+
+ __u32 refcount;
+ __u32 namelen;
+
+ char name[1];
+};
+
+struct fuse {
+ __u64 next_generation;
+ __u64 next_node_id;
+
+ int fd;
+
+ struct node *all;
+
+ struct node root;
+ char rootpath[1024];
+};
+
+#define PATH_BUFFER_SIZE 1024
+
+char *node_get_path(struct node *node, char *buf, const char *name)
+{
+ char *out = buf + PATH_BUFFER_SIZE - 1;
+ int len;
+ out[0] = 0;
+
+ if (name) {
+ len = strlen(name);
+ goto start;
+ }
+
+ while (node) {
+ name = node->name;
+ len = node->namelen;
+ node = node->parent;
+ start:
+ if ((len + 1) > (out - buf))
+ return 0;
+ out -= len;
+ memcpy(out, name, len);
+ out --;
+ out[0] = '/';
+ }
+
+ return out;
+}
+
+void attr_from_stat(struct fuse_attr *attr, struct stat *s)
+{
+ attr->ino = s->st_ino;
+ attr->size = s->st_size;
+ attr->blocks = s->st_blocks;
+ /* TODO: time */
+ attr->mode = s->st_mode;
+ attr->nlink = s->st_nlink;
+ /* TODO: uid/gid */
+
+ attr->uid = 1000;
+ attr->gid = 1000;
+}
+
+int node_get_attr(struct node *node, struct fuse_attr *attr)
+{
+ int res;
+ struct stat s;
+ char *path, buffer[PATH_BUFFER_SIZE];
+
+ path = node_get_path(node, buffer, 0);
+ res = lstat(path, &s);
+ if (res < 0) {
+ ERROR("lstat('%s') errno %d\n", path, errno);
+ return -1;
+ }
+
+ attr_from_stat(attr, &s);
+ attr->ino = node->nid;
+
+ return 0;
+}
+
+struct node *node_create(struct node *parent, const char *name, __u64 nid, __u64 gen)
+{
+ struct node *node;
+ int namelen = strlen(name);
+
+ node = calloc(1, sizeof(struct node) + namelen);
+ if (node == 0) {
+ return 0;
+ }
+
+ node->nid = nid;
+ node->gen = gen;
+ node->parent = parent;
+ node->next = parent->child;
+ parent->child = node;
+ memcpy(node->name, name, namelen + 1);
+ node->namelen = namelen;
+ parent->refcount++;
+
+ return node;
+}
+
+void fuse_init(struct fuse *fuse, int fd, const char *path)
+{
+ fuse->fd = fd;
+ fuse->next_node_id = 2;
+ fuse->next_generation = 0;
+
+ fuse->all = &fuse->root;
+
+ fuse->root.nid = FUSE_ROOT_ID; /* 1 */
+ fuse->root.next = 0;
+ fuse->root.child = 0;
+ fuse->root.parent = 0;
+
+ fuse->root.all = 0;
+ fuse->root.refcount = 2;
+
+ strcpy(fuse->root.name, path);
+ fuse->root.namelen = strlen(fuse->root.name);
+}
+
+static inline void *id_to_ptr(__u64 nid)
+{
+ return (void *) nid;
+}
+
+static inline __u64 ptr_to_id(void *ptr)
+{
+ return (__u64) ptr;
+}
+
+
+struct node *lookup_by_inode(struct fuse *fuse, __u64 nid)
+{
+ if (nid == FUSE_ROOT_ID) {
+ return &fuse->root;
+ } else {
+ return id_to_ptr(nid);
+ }
+}
+
+struct node *lookup_child_by_name(struct node *node, const char *name)
+{
+ for (node = node->child; node; node = node->next) {
+ if (!strcmp(name, node->name)) {
+ return node;
+ }
+ }
+ return 0;
+}
+
+struct node *lookup_child_by_inode(struct node *node, __u64 nid)
+{
+ for (node = node->child; node; node = node->next) {
+ if (node->nid == nid) {
+ return node;
+ }
+ }
+ return 0;
+}
+
+struct node *node_lookup(struct fuse *fuse, struct node *parent, const char *name,
+ struct fuse_attr *attr)
+{
+ int res;
+ struct stat s;
+ char *path, buffer[PATH_BUFFER_SIZE];
+ struct node *node;
+
+ path = node_get_path(parent, buffer, name);
+ /* XXX error? */
+
+ res = lstat(path, &s);
+ if (res < 0)
+ return 0;
+
+ node = lookup_child_by_name(parent, name);
+ if (!node) {
+ node = node_create(parent, name, fuse->next_node_id++, fuse->next_generation++);
+ if (!node)
+ return 0;
+ node->nid = ptr_to_id(node);
+ node->all = fuse->all;
+ fuse->all = node;
+ }
+
+ attr_from_stat(attr, &s);
+ attr->ino = node->nid;
+
+ return node;
+}
+
+void node_release(struct node *node)
+{
+ TRACE("RELEASE %p (%s) rc=%d\n", node, node->name, node->refcount);
+ node->refcount--;
+ if (node->refcount == 0) {
+ if (node->parent->child == node) {
+ node->parent->child = node->parent->child->next;
+ } else {
+ struct node *node2;
+
+ node2 = node->parent->child;
+ while (node2->next != node)
+ node2 = node2->next;
+ node2->next = node->next;
+ }
+
+ TRACE("DESTROY %p (%s)\n", node, node->name);
+
+ node_release(node->parent);
+
+ node->parent = 0;
+ node->next = 0;
+
+ /* TODO: remove debugging - poison memory */
+ memset(node, 0xef, sizeof(*node) + strlen(node->name));
+
+ free(node);
+ }
+}
+
+void fuse_status(struct fuse *fuse, __u64 unique, int err)
+{
+ struct fuse_out_header hdr;
+ hdr.len = sizeof(hdr);
+ hdr.error = err;
+ hdr.unique = unique;
+ if (err) {
+// ERROR("*** %d ***\n", err);
+ }
+ write(fuse->fd, &hdr, sizeof(hdr));
+}
+
+void fuse_reply(struct fuse *fuse, __u64 unique, void *data, int len)
+{
+ struct fuse_out_header hdr;
+ struct iovec vec[2];
+ int res;
+
+ hdr.len = len + sizeof(hdr);
+ hdr.error = 0;
+ hdr.unique = unique;
+
+ vec[0].iov_base = &hdr;
+ vec[0].iov_len = sizeof(hdr);
+ vec[1].iov_base = data;
+ vec[1].iov_len = len;
+
+ res = writev(fuse->fd, vec, 2);
+ if (res < 0) {
+ ERROR("*** REPLY FAILED *** %d\n", errno);
+ }
+}
+
+void lookup_entry(struct fuse *fuse, struct node *node,
+ const char *name, __u64 unique)
+{
+ struct fuse_entry_out out;
+
+ memset(&out, 0, sizeof(out));
+
+ node = node_lookup(fuse, node, name, &out.attr);
+ if (!node) {
+ fuse_status(fuse, unique, -ENOENT);
+ return;
+ }
+
+ node->refcount++;
+// fprintf(stderr,"ACQUIRE %p (%s) rc=%d\n", node, node->name, node->refcount);
+ out.nodeid = node->nid;
+ out.generation = node->gen;
+ out.entry_valid = 10;
+ out.attr_valid = 10;
+
+ fuse_reply(fuse, unique, &out, sizeof(out));
+}
+
+void handle_fuse_request(struct fuse *fuse, struct fuse_in_header *hdr, void *data, unsigned len)
+{
+ struct node *node;
+
+ if ((len < sizeof(*hdr)) || (hdr->len != len)) {
+ ERROR("malformed header\n");
+ return;
+ }
+
+ len -= hdr->len;
+
+ if (hdr->nodeid) {
+ node = lookup_by_inode(fuse, hdr->nodeid);
+ if (!node) {
+ fuse_status(fuse, hdr->unique, -ENOENT);
+ return;
+ }
+ } else {
+ node = 0;
+ }
+
+ switch (hdr->opcode) {
+ case FUSE_LOOKUP: { /* bytez[] -> entry_out */
+ TRACE("LOOKUP %llx %s\n", hdr->nodeid, (char*) data);
+ lookup_entry(fuse, node, (char*) data, hdr->unique);
+ return;
+ }
+ case FUSE_FORGET: {
+ struct fuse_forget_in *req = data;
+ TRACE("FORGET %llx (%s) #%lld\n", hdr->nodeid, node->name, req->nlookup);
+ /* no reply */
+ while (req->nlookup--)
+ node_release(node);
+ return;
+ }
+ case FUSE_GETATTR: { /* getattr_in -> attr_out */
+ struct fuse_getattr_in *req = data;
+ struct fuse_attr_out out;
+
+ TRACE("GETATTR flags=%x fh=%llx\n",req->getattr_flags, req->fh);
+
+ memset(&out, 0, sizeof(out));
+ node_get_attr(node, &out.attr);
+ out.attr_valid = 10;
+
+ fuse_reply(fuse, hdr->unique, &out, sizeof(out));
+ return;
+ }
+ case FUSE_SETATTR: { /* setattr_in -> attr_out */
+ struct fuse_setattr_in *req = data;
+ struct fuse_attr_out out;
+ TRACE("SETATTR fh=%llx id=%llx valid=%x\n",
+ req->fh, hdr->nodeid, req->valid);
+
+ /* XXX */
+
+ memset(&out, 0, sizeof(out));
+ node_get_attr(node, &out.attr);
+ out.attr_valid = 10;
+ fuse_reply(fuse, hdr->unique, &out, sizeof(out));
+ return;
+ }
+// case FUSE_READLINK:
+// case FUSE_SYMLINK:
+ case FUSE_MKNOD: { /* mknod_in, bytez[] -> entry_out */
+ struct fuse_mknod_in *req = data;
+ char *path, buffer[PATH_BUFFER_SIZE];
+ char *name = ((char*) data) + sizeof(*req);
+ int res;
+ TRACE("MKNOD %s @ %llx\n", name, hdr->nodeid);
+ path = node_get_path(node, buffer, name);
+
+ req->mode = (req->mode & (~0777)) | 0664;
+ res = mknod(path, req->mode, req->rdev); /* XXX perm?*/
+ if (res < 0) {
+ fuse_status(fuse, hdr->unique, -errno);
+ } else {
+ lookup_entry(fuse, node, name, hdr->unique);
+ }
+ return;
+ }
+ case FUSE_MKDIR: { /* mkdir_in, bytez[] -> entry_out */
+ struct fuse_mkdir_in *req = data;
+ struct fuse_entry_out out;
+ char *path, buffer[PATH_BUFFER_SIZE];
+ char *name = ((char*) data) + sizeof(*req);
+ int res;
+ TRACE("MKDIR %s @ %llx 0%o\n", name, hdr->nodeid, req->mode);
+ path = node_get_path(node, buffer, name);
+
+ req->mode = (req->mode & (~0777)) | 0775;
+ res = mkdir(path, req->mode);
+ if (res < 0) {
+ fuse_status(fuse, hdr->unique, -errno);
+ } else {
+ lookup_entry(fuse, node, name, hdr->unique);
+ }
+ return;
+ }
+ case FUSE_UNLINK: { /* bytez[] -> */
+ char *path, buffer[PATH_BUFFER_SIZE];
+ int res;
+ TRACE("UNLINK %s @ %llx\n", (char*) data, hdr->nodeid);
+ path = node_get_path(node, buffer, (char*) data);
+ res = unlink(path);
+ fuse_status(fuse, hdr->unique, res ? -errno : 0);
+ return;
+ }
+ case FUSE_RMDIR: { /* bytez[] -> */
+ char *path, buffer[PATH_BUFFER_SIZE];
+ int res;
+ TRACE("RMDIR %s @ %llx\n", (char*) data, hdr->nodeid);
+ path = node_get_path(node, buffer, (char*) data);
+ res = rmdir(path);
+ fuse_status(fuse, hdr->unique, res ? -errno : 0);
+ return;
+ }
+ case FUSE_RENAME: { /* rename_in, oldname, newname -> */
+ struct fuse_rename_in *req = data;
+ char *oldname = ((char*) data) + sizeof(*req);
+ char *newname = oldname + strlen(oldname) + 1;
+ char *oldpath, oldbuffer[PATH_BUFFER_SIZE];
+ char *newpath, newbuffer[PATH_BUFFER_SIZE];
+ struct node *newnode;
+ int res;
+
+ newnode = lookup_by_inode(fuse, req->newdir);
+ if (!newnode) {
+ fuse_status(fuse, hdr->unique, -ENOENT);
+ return;
+ }
+
+ oldpath = node_get_path(node, oldbuffer, oldname);
+ newpath = node_get_path(newnode, newbuffer, newname);
+
+ res = rename(oldpath, newpath);
+ fuse_status(fuse, hdr->unique, res ? -errno : 0);
+ return;
+ }
+// case FUSE_LINK:
+ case FUSE_OPEN: { /* open_in -> open_out */
+ struct fuse_open_in *req = data;
+ struct fuse_open_out out;
+ char *path, buffer[PATH_BUFFER_SIZE];
+ struct handle *h;
+
+ h = malloc(sizeof(*h));
+ if (!h) {
+ fuse_status(fuse, hdr->unique, -ENOMEM);
+ return;
+ }
+
+ path = node_get_path(node, buffer, 0);
+ TRACE("OPEN %llx '%s' 0%o fh=%p\n", hdr->nodeid, path, req->flags, h);
+ h->fd = open(path, req->flags);
+ if (h->fd < 0) {
+ ERROR("ERROR\n");
+ fuse_status(fuse, hdr->unique, errno);
+ free(h);
+ return;
+ }
+ out.fh = ptr_to_id(h);
+ out.open_flags = 0;
+ out.padding = 0;
+ fuse_reply(fuse, hdr->unique, &out, sizeof(out));
+ return;
+ }
+ case FUSE_READ: { /* read_in -> byte[] */
+ char buffer[128 * 1024];
+ struct fuse_read_in *req = data;
+ struct handle *h = id_to_ptr(req->fh);
+ int res;
+ TRACE("READ %p(%d) %u@%llu\n", h, h->fd, req->size, req->offset);
+ if (req->size > sizeof(buffer)) {
+ fuse_status(fuse, hdr->unique, -EINVAL);
+ return;
+ }
+ res = pread(h->fd, buffer, req->size, req->offset);
+ if (res < 0) {
+ fuse_status(fuse, hdr->unique, errno);
+ return;
+ }
+ fuse_reply(fuse, hdr->unique, buffer, res);
+ return;
+ }
+ case FUSE_WRITE: { /* write_in, byte[write_in.size] -> write_out */
+ struct fuse_write_in *req = data;
+ struct fuse_write_out out;
+ struct handle *h = id_to_ptr(req->fh);
+ int res;
+ TRACE("WRITE %p(%d) %u@%llu\n", h, h->fd, req->size, req->offset);
+ res = pwrite(h->fd, ((char*) data) + sizeof(*req), req->size, req->offset);
+ if (res < 0) {
+ fuse_status(fuse, hdr->unique, errno);
+ return;
+ }
+ out.size = res;
+ fuse_reply(fuse, hdr->unique, &out, sizeof(out));
+ goto oops;
+ }
+// case FUSE_STATFS:
+ case FUSE_RELEASE: { /* release_in -> */
+ struct fuse_release_in *req = data;
+ struct handle *h = id_to_ptr(req->fh);
+ TRACE("RELEASE %p(%d)\n", h, h->fd);
+ close(h->fd);
+ free(h);
+ fuse_status(fuse, hdr->unique, 0);
+ return;
+ }
+// case FUSE_FSYNC:
+// case FUSE_SETXATTR:
+// case FUSE_GETXATTR:
+// case FUSE_LISTXATTR:
+// case FUSE_REMOVEXATTR:
+ case FUSE_FLUSH:
+ fuse_status(fuse, hdr->unique, 0);
+ return;
+ case FUSE_OPENDIR: { /* open_in -> open_out */
+ struct fuse_open_in *req = data;
+ struct fuse_open_out out;
+ char *path, buffer[PATH_BUFFER_SIZE];
+ struct dirhandle *h;
+
+ h = malloc(sizeof(*h));
+ if (!h) {
+ fuse_status(fuse, hdr->unique, -ENOMEM);
+ return;
+ }
+
+ path = node_get_path(node, buffer, 0);
+ TRACE("OPENDIR %llx '%s'\n", hdr->nodeid, path);
+ h->d = opendir(path);
+ if (h->d == 0) {
+ ERROR("ERROR\n");
+ fuse_status(fuse, hdr->unique, -errno);
+ free(h);
+ return;
+ }
+ out.fh = ptr_to_id(h);
+ fuse_reply(fuse, hdr->unique, &out, sizeof(out));
+ return;
+ }
+ case FUSE_READDIR: {
+ struct fuse_read_in *req = data;
+ char buffer[8192];
+ struct fuse_dirent *fde = (struct fuse_dirent*) buffer;
+ struct dirent *de;
+ struct dirhandle *h = id_to_ptr(req->fh);
+ TRACE("READDIR %p\n", h);
+ de = readdir(h->d);
+ if (!de) {
+ fuse_status(fuse, hdr->unique, 0);
+ return;
+ }
+ fde->ino = FUSE_UNKNOWN_INO;
+ fde->off = 0;
+ fde->type = de->d_type;
+ fde->namelen = strlen(de->d_name);
+ memcpy(fde->name, de->d_name, fde->namelen + 1);
+ fuse_reply(fuse, hdr->unique, fde,
+ FUSE_DIRENT_ALIGN(sizeof(struct fuse_dirent) + fde->namelen));
+ return;
+ }
+ case FUSE_RELEASEDIR: { /* release_in -> */
+ struct fuse_release_in *req = data;
+ struct dirhandle *h = id_to_ptr(req->fh);
+ TRACE("RELEASEDIR %p\n",h);
+ closedir(h->d);
+ free(h);
+ fuse_status(fuse, hdr->unique, 0);
+ return;
+ }
+// case FUSE_FSYNCDIR:
+ case FUSE_INIT: { /* init_in -> init_out */
+ struct fuse_init_in *req = data;
+ struct fuse_init_out out;
+
+ TRACE("INIT ver=%d.%d maxread=%d flags=%x\n",
+ req->major, req->minor, req->max_readahead, req->flags);
+
+ out.major = FUSE_KERNEL_VERSION;
+ out.minor = FUSE_KERNEL_MINOR_VERSION;
+ out.max_readahead = req->max_readahead;
+ out.flags = 0;
+ out.max_background = 32;
+ out.congestion_threshold = 32;
+ out.max_write = 256 * 1024;
+
+ fuse_reply(fuse, hdr->unique, &out, sizeof(out));
+ return;
+ }
+ default: {
+ struct fuse_out_header h;
+ ERROR("NOTIMPL op=%d uniq=%llx nid=%llx\n",
+ hdr->opcode, hdr->unique, hdr->nodeid);
+
+ oops:
+ h.len = sizeof(h);
+ h.error = -ENOSYS;
+ h.unique = hdr->unique;
+ write(fuse->fd, &h, sizeof(h));
+ break;
+ }
+ }
+}
+
+void handle_fuse_requests(struct fuse *fuse)
+{
+ unsigned char req[256 * 1024 + 128];
+ int len;
+
+ for (;;) {
+ len = read(fuse->fd, req, 8192);
+ if (len < 0) {
+ if (errno == EINTR)
+ continue;
+ ERROR("handle_fuse_requests: errno=%d\n", errno);
+ return;
+ }
+ handle_fuse_request(fuse, (void*) req, (void*) (req + sizeof(struct fuse_in_header)), len);
+ }
+}
+
+int main(int argc, char **argv)
+{
+ struct fuse fuse;
+ char opts[256];
+ int fd;
+ int res;
+ unsigned uid;
+ unsigned gid;
+ const char *path;
+
+ if (argc != 4) {
+ ERROR("usage: sdcard <path> <uid> <gid>\n");
+ return -1;
+ }
+
+ uid = strtoul(argv[2], 0, 10);
+ gid = strtoul(argv[3], 0, 10);
+ if (!uid || !gid) {
+ ERROR("uid and gid must be nonzero\n");
+ return -1;
+ }
+
+ path = argv[1];
+
+ /* cleanup from previous instance, if necessary */
+ umount2("/sdcard", 2);
+
+ fd = open("/dev/fuse", O_RDWR);
+ if (fd < 0){
+ ERROR("cannot open fuse device (%d)\n", errno);
+ return -1;
+ }
+
+ sprintf(opts, "fd=%i,rootmode=40000,default_permissions,allow_other,"
+ "user_id=%d,group_id=%d", fd, uid, gid);
+
+ res = mount("/dev/fuse", "/sdcard", "fuse", MS_NOSUID | MS_NODEV, opts);
+ if (res < 0) {
+ ERROR("cannot mount fuse filesystem (%d)\n", errno);
+ return -1;
+ }
+
+ if (setgid(gid) < 0) {
+ ERROR("cannot setgid!\n");
+ return -1;
+ }
+ if (setuid(uid) < 0) {
+ ERROR("cannot setuid!\n");
+ return -1;
+ }
+
+ fuse_init(&fuse, fd, path);
+
+ umask(0);
+ handle_fuse_requests(&fuse);
+
+ return 0;
+}